1. Field of the Invention
The present invention relates to a method for manufacturing a hollow fiber reinforced thermoplastic resin molded article. In the case where joining a plurality of component materials consisting of fiber reinforced thermoplastic resin, with the method of the present invention, by affixing reinforcing pieces consisting of a fiber reinforced thermoplastic prepreg to the junctions along which the component materials are joined, housing of this within a mold as a provisional assembly and then forming a joined unitary body by increasing the internal pressure within the mold while heating, it is possible to efficiently manufacture a complicatedly shaped hollow article excelling in mechanical strength.
2. Related Art
As a manufacturing method for a hollow article such as a golf club head or the like, a method has been proposed wherein component materials, of which shapes obtained by partitioning the approximate shape of the head into two or more parts, are formed out of a fiber reinforced thermoplastic resin prepreg, and inserted into a mold as a provisional assembly. This then is heated and molded as the internal pressure is increased. FIGS. 6 and 7 show an example of this manufacturing method for a golf club head (hereinafter referred to simply as "head"). FIG. 6 is a perspective view showing an example of the shapes of the component materials, while FIG. 7 is an explanatory diagram showing the condition wherein a component material is inserted into a mold. The numerals 11, 12, 13, and 14 in the figures represent, respectively, the component material, the face surface of the head, the sole, and the crown.
In the manufacture of such a hollow article as this head, a prepreg in the form of a sheet of a desired thickness is first prepared. By deep drawing, the prepreg is shaped into each of the component materials 11 which form each of a face surface 12, a sole 13, and a crown 14 as are shown in FIG. 6. Further, at an optional position on the component material 11, a through opening 15 is provided for adding pressure to the internal portion of the head.
Next, the obtained component materials 11 are placed within the mold as a provisional assembly as is shown in FIG. 7. The inner surface of the mold is a hollow body having the shape of the head. A through opening 16 is provided at an optional position of the mold and is constructed so that pressure may be added to the internal portion of the head by introducing a medium for adding pressure within the head from the through opening 16. Further, this mold 17 is entirely housed within a vacuum heating device which is not shown in the figures.
Moreover, to the inner side of the provisional assembly of the component materials 11 there is inserted a balloon 18 consisting of silicone resin or the like. The mouth of this balloon 18 is connected to a pressure device, not shown in the figures, via the through opening 15 of the component material 11 and the through opening 16 of the mold 17.
In this condition, the vacuum heating device in which mold 17 is housed is evacuated of air so that the pressure in the space formed between the component materials 11 and the mold 17 is reduced. Further, the pressure within the balloon 18 is increased by introduction of a medium for adding pressure such as nitrogen gas or the like, while at the same time heating is carried out.
As a result of this heating, the component materials 11 are again melted while at the same time, because of evacuation and addition of pressure, there is an application of force directed from the inside to the outside of the component materials 11. Accordingly, the radial dimensions increase and component materials 11 are molded to a shape corresponding to the shape of the inner surface of the mold 17.
Further, following cooling of the mold 17, the pressure state is lifted, the balloon 18 is extracted, and the mold 17 is removed. Consequently, a head-shaped hollow body is obtained.
When forming a hollow molded article by this method, an overlapping portion (denoted by the symbol L in the figure) may be provided by forming a tapered portion, a step portion, or a grooved portion on the end surface of the junction of each component material 11 as is shown in FIG. 8 so that a certain degree of strength can be obtained in the junctions.
However, although a certain degree of strength can be obtained with this type of joining method, when a great deal of force is applied there is a possibility that damage will be incurred at the junctions. Accordingly, a further improvement in strength was desired.